Methods of forming soft solder joints

ABSTRACT

In the art of forming soft solder sweat joints connecting tubular copper members, the method of introducing into the joint are around one of the members a solder-reinforcing agent consisting of copper, and thereafter introducing a molten soft solder.

Max:119; (3, RAYNEs ETAL 3,568,304

METHODS OF FORMING SOFT SIOLDER JOINTS Original Filed Nov. 1965 I 4Sheets-Sheet 1 TEST SPECIMEN 1 O. 3 2 mm TlME--HOURS DATA l/2'M COPPERTUBING I 3 WROUGHT & 3 CAST COUPLINGS 66% COPPER SHEAR. 37o LB/IN LOAD:8.?- LB.

TEST SPECIMEN-#2- O O 3 2 W 0 $5 zoazwtm TIME HOURS v DATA I/2 M COPPERTUBING 3 WROUGHT 8 3 CAST COUPLINGS 66 /o COPPER INVENTORfi 57o LBHNEBERTRAM C. RAYNES LOAD: I45 LB.

MICHAEL PESCATRICE IMMCh 9, 1971 RAYNES EI'AL 04 METHODS 01 FORMING SOFTSOLDER JOINTS v Original Filed Nov; 22, 1965 Y 4 Sheets-Sheet 2 TESTSPECIMEN *3 g F 1g. 3

' TlME-'HOURS v .DATA

v2 M COPPER TUBING 3 WROUGHT 8 3 CAST COUPLINGS 50 "/0 COPPER a SHEAR=31o LB/IN LOAD.=8.8 -LB.

" TEST SPECIMEN 4 .030 If) LU I v U F lg. 4 Gfloio TIME-HOURS l/2MCOPPER TUBING 3 WROUGHT a 3 CAST COUPLINGS 50% COPPER SHEAR; s05 LEAN?LOADI I60 LB.

INVENTORSP BERTRAM c. RAYNES MICHAEL PESCATRICE u IMF. M

March 9, 1971 Original Filed Nov. 22, 1965 EX TENSONf INCHES '5. RAYNES3,568,304

METHODS OF FORMING SOFT SOLDER JOINTS QOIO EXTENSION- tNCHES 4 Sheets-Sheet 5 TEST SPECIMEN#5.

Fig.5

2000 4000 TlME HOURS DATA v 1/2 M COPPER Tuamc 3 WROUGHT a 3 CAST couuwes 34% COPPER SHEARI 370 LB./IN.2

LOAD: as

TEST" SPECIMEN 6 Fig. 6

2000 4000 0000 I TI MEHOURS DATA 1/2 M COPPER meme 3 WROUGHT a 3 CASTcou uwes 34 /o COPPER 2 SHEAR 595 LB/ IN. 'NVENTO 3: LOAD 15.6 LB BERTRAM C. RAYN 5 MICHAEL PESCATRICE c, R YNE ETAL 3,568,304

METHODS OF FORMING SO F'I' SOLDER JOINTS Original Filed'Nov. 22,1965 4Sheets-Sheet 4.

TEST SPECIMEN 7 LL! .5 3 g z .020 9* (I) 5.0m F 7 T|ME- 0u s DATA 0 1/2M ,COPP'ERTUBING" s WROUGHT a 3 CAST COUPLINGS 20% COPPER 2 SHEAR!370LB./|IN LOADI 8.? LB.

' I ,1 TEST SPECIMEN a 030 I l g 1 .020 1 I 0 2 .00 F lg. 8 I

TIME-HOURS DATA 1/2' M COPPER TUBING 3WROUGHT a 3 CAST COUPLINGS 20%COPPER SHE/M 605 LB/IN mam-ow BERTRAM c. RAYNES LOAD MICHAEL PESCATRICEwarf w P United States Patent 3,568,304 METHODS OF FORMING SOFT SOLDERJOINTS Bertram C. Raynes, Pepper Pike, and Michael Peseatrice, Lakewood,Ohio, assignors to Nibco Inc., Elkhart, Ind. Original application Nov.22, 1965, Ser. No. 509,053, now Patent No. 3,418,179, dated Dec. 24,1968. Divided and this application May 17, 1968, Ser. No. 729,981 Int.CI. 15231: 31/02 US. Cl. 29--489 14 Claims ABSTRACT OF THE DISCLOSURE Inthe art of forming soft solder sweat joints connecting tubular coppermembers, the method of introducing into the joint area around one of themembers a solderreinforcing agent consisting of copper, and thereafterintroducing a molten soft solder.

CROSS-REFERENCE TO RELATED APPLICATION This application is a division ofapplication Ser. No. 509,053 of Bertram C. Raynes et al., filed Nov. 22,1965 and entitled Soft Solder Joints and Methods and Materials forProducing the Same, now Pat. No. 3,418,179.

BACKGROUND OF THE INVENTION This invention relates generally to thesoldering art, and more specifically to the formation of soft solderjoints. It is particularly concerned with methods for forming sweatjoints connecting copper fittings and tubing such as those found inplumbing systems.

The resistance of a soft solder joint to substantially constant orstatic forces as distinguished from transient forces, is known as creepstrength. Because of its poor creep strength which may be less thanone-eighteenth of the short term loading of the joint, the soft soldersweat joint is the Weakest part of the present copper plumbing systems.This weakness in soft solder sweat joints results primarily from the lowstrength of current solder materials. It is believed this weakness isalso due to defects in the form of voids which occur in the solderspace.

Prior efforts have had little success in either increasing the strengthof solder materials and joints or improving their solderability todecrease the occurrence of joint defects. Instead, copper plumbingsystems, as they are now generally assembled and constituted, are overdesigned structurally, particularly in the length of the solder cup, inan effort to assure adequate all-over joint strength. Some idea of thisover design may be had by noting that the 50-50 soft solder sweat jointcreep load for onehalf inch size plumbing is on the order of one hundredpounds in hot water service, while the creep load for the copper tubeand fittings themselves is on the order of three thousand pounds ormore, a factor of thirty or greater. The factor is greater still forlarger size plumbing.

In spite of the over design of the solder cup to provide greater totalstrength in the joints, the unit creep strength afforded by the presentsolder materials is so low that the conventional soft solder jointoperates at a calculated safety factor level of 2.8 which is one of thelowest in building construction. If the long term joint strength inconventional systems were to have a safety factor equivalent to that inthe rest of the system, the length of the solder cup would have to beseveral times its present length.

The actual creep strength of sweat joints formed by conventionalmaterials and techniques is often less than the calculated or ratedstrength because of voids occurice ring in the solder space. Suchdefects are found in systems installed by expert plumbers and are quitecommon in joints made by relatively unskilled persons. The mechanismsresponsible for defect formations are numerous, but it has beendiscovered that poor surface wetting and rate of spreading of the solderand a capillary driving force which is insutficient completely to expelthe flux from the joint and promote a complete fill are prominentfactors.

It Will be apparent from the foregoing that important advantages can beobtained by increasing the creep strength of a soft solder sweat joint.An improvement in the unit creep strength would improve the entiregeneral strength of sweat plumbing systems. Concomitantly, it would bepossible to eliminate much of the conventional over design by decreasingthe solder cup length, as well as lightening other components includingthe tubing, and thereby provide for substantial cost reductions. Animprovement in the joint strength would also afford increasedreliability and safety factor and reduce the occurrence of servicefailures.

Known prior art joints, such as brazed joints, exist which havesubstantially greater creep strength than soft solder joints. Thesejoints require higher forming temperatures than do soft solder joints.This is a factor that may make brazed joints undesirable, especially inframe constructions where high temperatures may be dangerous. Thus, inspite of its poor creep strength, the soft solder joint is preferred andused because of ease of installation, its low temperature melting, andalso because of its good capillary flow characteristics at lowtemperatures.

SUMMARY OF THE INVENTION The copending application of Theodore D. Jaynesfor Soft Solder Joints, Ser. No. 509,070, filed Nov. 22, 1965 andassigned to the same assignee as the present application, disclosesbasic discoveries which have made it possible to obtain copper sweatjoints having unexpectedly high strength and to improve the overallstrength of copper plumbing systems. In general, the inventionsdescribed in that application contemplate the introductions of astrengthening agent into the joint in order to improve the strengthproperties of the solder layer. The strengthening agent is preferably inthe form of discrete particles which are unalloyed with the solder andare distributed throughout the joint. Several ways were disclosed forintroducing the particles into the joint, including theelectrodeposition of copper particles in the fitting, preplacing aquantity of particles in the fitting with a paste flux, and mixing orblending the particles in a suitable flux which is then applied in theusual manner to at least one of the parts to be joined.

The present invention is a novel advancement of the foregoing inventionsdisclosed in copending application Ser. No. 509,070. The inventionresides in the discovery that, in addition to affecting a markedincrease in the strength of soft solder materials, it is possible toimprove the solderability of sweat joints and substantially reduce oreliminate the occurrence of voids in the solder layer by controlling thesize and amount of the dispersion strengthening agent.

In carrying out the invention, the dispersion strengthening agent ispreferably introduced into the solder joint by a flux vehicle. This maybe accomplished by mixing or blending particles of the strengtheningagent in a suitable flux, such as a commercially available corrosivepaste flux, which is applied to the parts to be joined in the usual way.Alternate techniques for introducing the dispersion strengthening agentare set forth below. Copper powders have proved especially effective asthe strengthening agent, although it is contemplated that materials suchas glass or the like which Will not cause electrochemical corrosion of asolder-copper system could be used.

As much as 80% by weight of copper powders can be introduced into apaste flux and the flux wiped onto a fitting in a manner similar toconventional flux. The major portion of the powder remains in the jointto strengthen the subsequently applied solder; however, as distinguishedfrom prior attempts which have been made to add a strengthening agentdirectly to the solder, the application of the preferred copper powderin a fiux vehicle does not adversely affect the flow characteristics ofthe solder and the times and temperatures of soldering operation. Themethods of this invention utilizing the copper flux material thereforeresult in greatly improved strength characteristics of the formed jointand yet do not require significant modification of standard solderingpractices. The methods of the invention can be used without specialhandling by both skilled and unskilled persons to form improved coppersweat joints.

It has been discovered that the optimum minimum amount of the dispersionstrengthening agent should be on the order of about 20% by weight in theflux and that the minimum particle size distribution should be about 85%or less minus 325 mesh. Examination of sweat joints made by use of aflux compound containing from about 20% to about 80% by weight of copperpowder having a particle size distribution of 85% or less minus 325 meshindicate fewer microscopically visible voids and imperfections than injoints made according to other procedures. Large voids are almosteliminated. While the mechanism responsible for the substantialreduction of -voids in' the solder space is not clearly understood, itis believed that one prominent factor is an increase in the capillaryforce or dynamic action of the molten solder. This belief is based onobsenvations that the solder meniscus advances evenly through the jointsin such a manner as to almost completely expel flux sludges and avoidentrapment of flux and gas. Thus, the use of distributed copperparticles promotes a complete fill of the joint by the molten solder andresults in a larger solder area than in conventional sweat joints of thesame size. The increased solder area is another reason for the greatlyimproved strength of joints made in accordance with this invention.

Accordingly, an object of the invention is to provide methods of makingsweat joints of improved strength. A more specific object of theinvention is to provide for the use of a dispersion strengthening agentin an amount and size which has been found effective to increase thestrength of the solder materials and to substantially reduce oreliminate the occurrence of voids in the solder layer.

7 Other features, objects, advantages and a fuller understanding of theinvention will be apparent from the following detailed description andthe accompanying drawmgs.

DESCRIPTION OF THE DRAWINGS In the drawings, FIGS. 1 through 8 aregraphs showing creep strength data of joints formed in accordance withthe invention compared to creep strength data of conventional coppersweat joints.

DESCRIPTION OF THE PREFERRED EMBODIMENT As generally described above,the invention is concerned with the formation of soft solder joints byuse of a strengthening agent which is in a form that is effective toincrease the strength of the solder material and to reduce theoccurrence of voids in the solder layer. In the preferred embodiments tobe described, the strengthening agent is in the form of discreteparticles which are added to the flux and the flux is applied to themetal parts in a manner similar to standard practice.

The primary matters of concern in carrying out the preferred concepts ofthe invention are the particular material selected as the strengtheningagent, the particle size, and the amount of particles added to the flux.The specific composition of the flux itself is not of significantimportance and various commercial fluxes can be selected depending uponthe particular soldering application. Similarly, the soft solder whichis used can be any conventional type.

In the specific examples set forth below, a conventional corrosive pasteflux sold under the trade name Oatey No. 5 by the L. R. Oatey 00.,Cleveland, Ohio was used as the vehicle for introducing the particlesinto the sweat joints. The soft solder used in forming the joints was a.standard 50-50 tin-lead solder. These materials were selected simplybecause they are presently Widely used in copper plumbing systems, andit is to be understood that the exemplary flux and solder are notlimiting of the invention.

A primary requirement of any commercially acceptable technique andmaterial for reinforcing copper sweat joints is to avoid altering thebasic solder-copper system by introducing a new metal atom that mightresult in electrochemical corrosion. Because of this consideration,commercially pure copper particles are a preferred strengthening agent,although it is contemplated that alloys containing copper could be used.Electrolytic copper powders which have a low percentage of alloyingelements and may be considered commercially pure are particularly wellsuited for the purposes of the present invention. While copper isdisclosed as a preferred strengthening material it is contemplated thatinert materials, such as glass particles or the like, which will notinduce corrosion or other detrimental actions in the joint could beused.

As noted above, another consideration inthe formation of reinforced,void-free soft solder joints is the particle size of the strengtheningagent. In forming sweat joints, the maximum particle size is determinedby clearance of the fitting. The average total clearance of most fittingdesigns is approximately 0.006 inch, and in such designs it is preferredthat the maximum particle size be 0.003 inch (100% minus 200 mesh).Particles having a maximum size of 0.003 inch can be distributed aroundthe end of the tube or the inside of the solder cup and the two membersmaintained in concentricity in accordance with good soldering practice.

In accordance with this invention, it has been determined that theminimum particle size distribution should be on the order of or lessminus 325 mesh. The most preferred powders which have been usedsuccessfully in the flux combinations have a maximum particle size ofapproximately .003 inch minus 200 mesh) and a minimum particle sizedistribution in the range of from about 50% to about 81% minus 325 meshwith the average minimum particle size being about 44 microns. Extremelyfinely divided powders, e.g. 100% minus 400 mesh, may have somestrengthening effect. However, it has been observed that joints formedwith such powders exhibit voids in the solder layer similar toconventional joints.

There are several commercially available copper powders which satisfythe foregoing parameter of particle size and can be used in accordancewith the invention. The following are three typical electrolytic copperpowders which have been used successfully:

(1) AMAX Type B electrolytic copper powder (American Metal Climax, Inc.)99.5 min. 01.1, apparent density 2.5-2.6 gm./cc.

Screen analysis:

(2) MD 201 granular copper powder (Metals Disintegratmg Corp.) 99.0% Cu,apparent density 2.4-2.8 gm./ cc.

Screen analysis, percent:

100% minus 200 mesh 85% minus 325 mesh (3) Screened electrolytic copperpowder.

Another parameter of the preferred copper-flux is the amount of copperpowder which is used. The preferred range of the copper powder or otherstrengthening agent in thefiux is from about by weight to about 80% byweight. While lesser amounts of copper powder may have somestrengthening effect on the solder, it has been found that when thepowder is below about 20% by weight in the flux the joints usuallyexhibit imperfections in the form of voids and are not visuallydifferent from unreinforced joints. Amounts of copper in excess of 80%also may provide improvements in the strength of the joints, but in suchinstances it is difiicult to wipe the copper-flux onto a fitting and thestiff flux may be stripped off when the tube is assembled in the cup.

Copper powder in the amounts indicated can be readily mixed or blendedinto the flux without requiring any special handling techniques orequipment. As noted above, the resulting composition has a long shelflife and can be stored for a year or more before use.

In use the copper-flux can be applied in nearly the same manner asconventional fluxes, although it has been observed that paste fluxescontaining large amounts of the powder apply somewhat more stiffiy thanthe usual paste flux. The subsequently introduced soft solder is readilyaccepted into the joint and the finished joint will have an exteriorappearance similar to that of an ordinary one. The soft solder may beplaced in the joint in accordance with conventional practices, such asmelting the solder by bringing it into contact with a surface heated tothe soldering temperature, allowing the molten solder to flow into andfill the joint space, and then cooling the metal surfaces. The inventionalso can be practiced in conjunction with the constructions and methodsdisclosed in copending applications Ser. No. 429,562, filed Feb. 1, 1965and entitled Sweat Soldering Apparatus, and Ser. No. 462,673, filed June9, 1965 and entitled Sweat Soldering Invention.

Accelerated screening creep tests of copper sweat joints formed by usingthe above-described copper-flux and method have shown a largeimprovement in the strength of the reinforced solder layer. Aspreviously discussed, this improvement is due in part to an increase inthe unit creep strength of the reinforced solder and also to thesubstantial elimination of voids in the solder space. In one suchaccelerated test, a test section of /2 inch wrought coupling jointsplaced under a load of 1000 pounds per square inch shear and containingthree conventional joints in which the solder was reinforced by acopper-flux containing 66% by weight of the copper indicated a minimumimprovement in strength of a factor of 7: 1. The maximum strengthimprovement has not been determined, since this test is still inprogress at the time of this writing. All three of the conventionallysoldered joints failed at the end of 292 test hours, the first havingfailed after only 101 hours. One of the copper-flux coupling jointsfailed after 725 hours, but all of the remaining reinforced couplingjoints have withstood over 3000 test hours.

Another accelerated test produced results similar to that set forthabove. In this test, a /2 inch wrought fitting was made using 66% byweight copper-flux. A shear load of 600 pounds per square inch wasapplied to the fitting 6 and the test is still in progress with no signof failure after over 4000 hours. A similar load on a conventional 50-50tin lead solder joint failed at the end of 1500 hours.

Extensive long term creep tests have also been conducted to show theimproved creep strength of copper reinforced sweat joints under longterm static shear loading. The test procedures which have been followedare similar to those described in the Building Materials and Structures(B MS) Report No. 58 by Swanger and Maupin, published Dec. 20, 1940 bythe National Bureau of Standards. For the most part, higher loads werechosen than by Swanger and Maupin because of the increased strength ofthe copper-flux joints and the desire to reduce the total test time.

The following table summarizes the long term test results of severalexamples of copper-flux joints made in accordance with this invention.In each of these examples, the copper powders were mixed in an Oatey No.5 corrosive paste flux referred to above. The copper powder was thepreviously described AMAX Type B electrolytic copper powder sold byAmerican Metal Climax, Inc. in which all powder larger than minus 200mesh (.003 inch) was screened out.

TABLE I Fitting Shear load in Cumu- Example size, Copper, pounds perNumber lative, Number inch percent square inch failures hours Referringto the drawings, FIGS. 1-8 show plotted data for each individual examplelisted above in the table in comparison with plotted data for eachindividual example listed above in the table in comparison with plotteddata calculated from the results of Swanger and Maupin. The solid linesin FIGS. 18 indicate the test results on the examples of the invention,while the dotted lines are based on the Swanger and Maupin data andindicate the average expected creep data for the test shear load orestimated data in the case of heavier loads.

The following Table II reports the results of modified short termtensile tests of conventional copper sweat joints and reinforced coppersweat joints made in accordance with this invention. By way ofexplaining the test procedures, it should be noted that ordinary tensiletesting by standard rates of applied stresses does not reveal much aboutthe strength of soldered joints. This is because the tube will failunder short term loads before the joint does unless there areextraordinary flaws in the joint. If a solid bar is substituted for thetubing, the fitting will frequently shear. Consequently, in conductingshort term tensile tests, the procedure 'was to reduce the solder areaof standard fittings by cutting down the cup length until the jointsfailed in the solder area. Joints of the same size were then made usingthe new copper flux and it was found that the average increase inreinforcement was from 10% to 15%.

AVE RA GE TENSILE 1 66% Cu and 34% flux.

It will be seen from the above that the strength improvement in theordinary copper sweat joints is substantial, and that this improvementcan be obtained in a practical and easily accomplished manner byapplying a flux containing the reinforcing agent to the parts to bejoined and then introducing amolten soft solder in the usual way. Thepreferred fiux which is used may be described broadly as flux vehiclecontaining from about to about 80% by Weight of the reinforcingparticles, which are preferably in the form of a copper powder, having aminimum particle size distribution of about 85% or less minus 325 meshand a maximum particle size Which does not exceed one-half of the totalclearance of the fitting design.

The finished joints may be broadly described as being characterized by adispersion throughout the solder layer of free particles, preferablycopper powder, having a minimum particle size distribution of about 85or less minus 325 mesh. While the preferred technique of introducing thepowder in the joints is by use of the novel flux, it is to be understoodthat copper particles of the specified size can be electrodeposited inthe fitting. It is also contemplated that copper powder or otherstrengthening material can be preplaced in the cup or fitting with apaste flux. 7

As used herein, the term free in referring to the dispersionstrengthening agent is intended to mean that the agent is substantiallyunalloyed in the solder layer. The term copper is used in thespecification and claims in a broad sense and includes commercially purecopper as well as metals and alloys containing copper.

Many modifications and variations of the invention will be apparent tothose skilled in the art in view of the foregoing detailed disclosure.Therefore, it is to be understood that, withinthe scope of the appendedclaims, the invention can be practiced otherwise than as specificallyshown and described.

What is claimed is:

1. A method of forming a soft solder sweat joint connecting coppermembers comprising the steps of applying to at least one of the membersa composition of matter consisting essentially of a mixture of a pasteflux and from about 20% to about 80% by weight copper particles having amesh size of 85% or less minus 325 mesh, subsequently introducing amolten soft solder, and thereafter allowing the solder to cool and forma joint between the members which is reinforced by free copper.

2. The method as claimed in claim 1 wherein said copper particles are acommercially pure, electrolytic copper powder.

3. The method as claimed in claim 1 wherein the copper particles have aminimum size in the range of from about 50% to about 81% minus 325 mesh.

4. The method as claimed in claim 3 wherein the copper particles have asize of 100% minus 200 mesh.

5. A method of forming a soft solder sweat joint connecting coppermembers comprising the steps of introduce ing into the joint areabetween said members a soft solder reinforcing material consisting ofcopper particles, the copper particles having a minimum size of 85% orless minus 325 mesh, subsequently introducing a molten soft solder, andthereafter allowing the solder to cool and form a joint between themembers which is reinforced by free copper.

6. The method as claimed in claim 5 wherein the copper particles areintroduced into the joint area by applying to at least one of themembers a paste flux containing the copper particles.

7. The method as claimed in claim 5 in which the copper particlesconsist of commercially pure, electrolytic copper powder.

8. The method as claimed in claimSwherein the copper particles have aminimumsize inthe range of from 50% to 8l%-minus 325 mesh. Y

9. The method as claimed in claim 5 in which the copper particles are100% minus 200 mesh.

10. The methodas claimed in claim 5 wherein the average minimum size ofthe copper particles is approximately 44 microns. j

11. A method. of forming a soft solder. sweat joint connecting coppermembers comprising the steps of applying to at least one of the membersa composition of matter consisting essentially of a paste flux anddiscrete particles of a solid, solder-reinforcing material which isinert t'o electrochemical action in a soft solder-copper system, thereinforcing material being present in the flux in an amount of from 20%to by weight and having a minimum size of or less minus 325 mesh.

12. The method as claimed in claim 11 in which the solder-reinforcingagent consists of copper particles.

13. A method of forming a soft solder sweat joint connecting coppermembers comprising the steps of applying to at least one of the membersa composition of matter consisting essentially of a paste flux anddiscrete particles of a solid, solder-reinforcing material which isinert to electrochemical action in a soft solder-copper system, thereinforcing material being present in the flux in an amount of from 20%to 80% by weight and having a particle size of minus 200 mesh and anaverage minimum particle size of approximately 44'micr ons.

14. The method as claimed in claim 13 in which the solder-reinforcingmaterial consists of copper particles.

References Cited UNITED STATES PATENTS 893,207 7/1908 Tabet 29-4961,722,025 7/1929 Wagener 29-495 1,966,260 7/1934 -Munson 29-4963,453,721 7/1969 Jayne z9 -4s9 JOHN F. CAMPBELL, Primary Examiner R. 'J.SHORE, Assistant Examiner i U.S. c1. X. R.' 29 192, 495, 503

